Pulsators of electromagnetic, mechanical, pneumatic, hydraulic and combined types are used nowadays to obtain pulsating loads in actuating mechanims. However, the most promising of all are hydraulic pulsators which can be used in manufacturing powerful equipment with pulsating loads.
The basic problem in the development of such equipment is the attainment of a great force in the actuating mechanisms, high frequency of load alternations, and efficiency. To this end, the pulsators must be of great capacity, quick-acting, leak-proof, capable of operating on water or aqueous emulsions and easily controlled.
The known basic types such as spool, valve, and plunger pulsators have not been widely employed in industry because of complicated circuits, poor reliability and short service life, difficulty in obtaining the required force and frequencies, low efficiency and incomplete unloading of the actuating member. The most up to date is the pulsator for hydraulic systems controlling actuating mechanisms, disclosed in U.S. Pat. No. 3,851,667 British Pat. No. 1,377,892.
The prior art pulsator comprises a housing accommodated coaxially in the cylindrical borings of which are a pusher, a delivery valve and a pneumatic piston displacing in the cavity communicating with the pneumatic control system. The housing has an upper cavity formed by the pusher piston, communicating with the high-pressure main and a lower cavity formed by the pusher piston, communicating with the actuating mechanism via a non-return valve.
As the fluid pressure in the system builds up, the specific pressure on the delivery valve chamfer of the prior art pulsator decreases since the pneumatic cylinder piston presses the delivery valve onto the chamfer with a constant force while the force under the pusher increases as the fluid pressure in the system becomes higher. When the force acting upon the pusher reaches about 50% of that developed by the pneumatic cylinder piston, the tight connection between the delivery valve chamfer and the seat becomes loose thus causing leaks of the working fluid which increase as result of a pressure built-up in the system. The working fluid leaks result in the increase of time required for producing pressure in the system and this prolongs the time of the technological cycle, reduces the efficiency of the press, leads to wear of the delivery valve and the valve seat.
In addition, when returning the fluid from the actuating mechanism the drive pumps also communicate with the return main which results in the reduction of the hydraulic system efficiency and the increase of the pulsator overall size because of the necessity to enlarge clear openings. With the control valve being open prior to the initiation of the actuating mechanism operation, an additional device should be provided to make the pusher piston lower cavity leak-proof as is the case with the control system disclosed in USSR Inventor's Certificate No. 506,514.